In the synthetic fiber industry, it is often necessary to backwind packages of bulked continuous filament yarn for additional operations, such as for air entangling multicomponent carpet yarn. When feed yarns having different colors or dye affinity, herein called "components", are backwound for air entangling, tension on the individual components affects the appearance of the final product. A low tension component will predominate because slightly more of it will be fed to the entangling point. This is especially true of crimped yarns which have an inherent springiness. U.S. Pat. No. 4,222,223 to Nelson illustrates the use of feed rate differential to create special effects. Sometimes, such as in U.S. Pat. No. 4,567,720 to Price, the feed of different components is varied at controlled time intervals to further enhance the effect.
The predominance of one component is not usually desirable. In many cases, therefore, component tensions must be accurately controlled at all times on all positions to produce uniformly combined yarn. Where tension differential allows one component to predominate, either temporarily or on one position, the yarn may produce streaks when used along with yarn produced from the same components but without tension differences. Streaks are particularly prevalent when components of contrasting colors, like red and green, are combined on multiple positions which unintentionally exhibit tension differences.
Unfortunately, tension differences are common in the backwinding operation. These differences can result from a number of factors such as creel position, friction on the running yarn at contact points, feed package size and build, physical properties such as bulk or finish level, etc. There are devices designed to address the problem of tension differential in separate yarn components. Some devices use pressure and friction. U.S. Pat. No. 3,797,775 to White discloses a device which establishes tension control by engaging the advancing filament with a rotor. The rotor is restrained from being driven by the advancing strand, thus tensioning the advancing strand. Another device making use of pressure and friction is shown in U.S. Pat. No. 4,343,146 to Nelson.
Other devices use electrical hysteresis to rectify tension differences. One such device is disclosed in U.S. Pat. No. 4,313,578 to Van Wilson et al. The Van Wilson device includes a manually adjustable tension setting tensiometer for adjusting a circuit to provide output voltages which select the tension values added to the advancing yarn.
Other devices control yarn tension by routing the yarn through a non-linear path. Exemplary is U.S. Pat. No. 3,191,885 to Jones et al. which describes a yarn tensioning device having a plurality of loops through which the yarn is threaded. The deviation of the yarn from the linear path is adjustable by pivoting an arm to which the loops are attached. Modifications on this general theme are illustrated in U.S. Pat. No. 3,010,270 to Richmond et al. and U.S. Pat. No. 4,697,317 to Nelson. Similarly, U.S. Pat. No. 3,609,835 to Boon teaches that friction may be used to provide somewhat controlled tension fluctuations.
Although the devices described above may be used to minimize tension differences between yarn components, they must be constantly monitored to guarantee tension uniformity. One reason for this is that feed yarn conditions constantly change. For example, the tension required to remove bulked continuous filament from a feed yarn package often depends on the package diameter. As the yarn is used, the package diameter continuously decreases thereby gradually continuously decreasing the tension of that component. When a full feed yarn package replaces an empty one, a discrete change in tension of the package component occurs. Even in a single position, many tension differences occur from package depletion and replacement. Other properties of individual feed yarn packages, such as density, yarn to yarn static friction due to crimp, constantly change component tensions, too.
There are devices which isolate component tension variations from the feed yarn package. For example, U.S. Pat. Nos. 3,411,548, 3,455,341, 3,759,300, all to Pfarrwaller, describe an apparatus for controlling the unwinding from a feed yarn package to isolate the tension variation at the feed yarn side. U.S. Pat. No. 4,351,495 to Lindstrom et al. describes another device which attempts to minimize tension fluctuation. U.S. Pat. No. 4,298,172 to Hellstrom describes an apparatus which enables thread to be wound onto the feed package in such a way that when unwound the variations in tension due to such unwinding are eliminated.
In addition, these feed yarn tension isolating devices can be used in combination with other tensioning devices, such as that shown in U.S. Pat. No. 3,191,885 to Jones et al., and the like. The result rather effectively eliminates multicomponent tension differences from the feed yarn package. But even the combination of devices does not compensate for other varying component properties, such as yarn bulk or finish. Furthermore, these devices are somewhat costly and typically require specialized maintenance and upkeep.
Other devices attempt to equalize component tensions by passing them together through a common tensioning device. One such device and process is shown in U.S. Pat. No. 4,570,312 to Whitener, Jr. The common device may reduce relative tension differences by increasing the tension level of all of the components. The equivalent increase causes the tension differential to be relatively less. For example, two components tensioned at 50 and 100 grams are relatively closer when increased to 550 and 600 grams tension. It is not usually desirable to operate a process at high tension levels. Overall tension increases can adversely affect a technique such as air entangling. Another drawback of such common tensioning devices is that they may magnify the effects of bulk or finish. For example, two components having different finish levels and entering the tensioning device at a uniform tension (perhaps both at 50 grams) may leave the device at 100 and 150 grams because the friction induced tension is greater on the component having less finish.
There remains a need for a manner of equalizing yarn component tensions without constant monitoring, expensive complicated hardware or excessive overall tension increases.